Field of the Invention
The present invention relates to a ketene imine compound, a polyester film, a back sheet for a solar cell module, and a solar cell module.
Background Art
A solar cell module generally has a laminate structure in which a glass or front sheet/a transparent filling material (sealing material)/a solar cell element/a sealing material/a back sheet are laminated in this order from the light-receiving surface side to which sunlight is incident. The solar cell element is generally embedded with a resin (sealing material) such as EVA (ethylene-vinyl acetate copolymer) or the like, and a protective sheet for a solar cell is further adhered thereto. In the protective sheet for a solar cell, in particular, a back sheet for a solar cell module which is disposed on the outermost layer protects the solar cell element. However, in a case where the solar cell module is installed on a stage, the back sheet is considered to be exposed to wind or rain, or to be placed under an environment of high temperature and high humidity for a long period of time, and therefore, excellent weather resistance is required.
As the back sheet for a solar cell module, in the related art, a polyester film, in particular, a polyethylene terephthalate (hereinafter, referred to as PET) film has been used. The polyester film has excellent heat resistance, mechanical characteristics, chemical resistance, and the like, and therefore, the polyester film is preferably used in the back sheet for a solar cell module. However, since the film has poor hydrolysis resistance, the molecular weight is reduced by hydrolysis, and mechanical properties are reduced by progressively stiffening, and thus, it is not possible to maintain a practical strength for a long period of time as a back sheet for a solar cell.
Patent Document 1 and Patent Document 2 propose to add a ketene imine compound as a terminal blocking agent to the polyester film in order to increase the hydrolysis resistance of the polyester film. Here, the ketene imine compound suppresses hydrolysis of polyester by reacting with the terminal carboxyl group of the polyester.